This invention relates generally to docking systems of the type typically used to facilitate the alignment of a towing vehicle with respect to a towed vehicle that is to be coupled thereto and, more particularly, to a precision line guided system that enables the operator of the towing vehicle to position it for coupling to the towed vehicle without outside assistance. Usually, the hitch or other coupling members of the two vehicles are not in view of the operator of the towing vehicle as it is being maneuvered into position for attachment to the towed vehicle.
A tensioned line guided system offers the best basis for a precision docking system. However, continuous lateral misalignment sensing between an actual and a desired vehicle path poses serious problems in practical systems. Major design considerations in such systems include the axial tension in the line that is required to actuate the alignment sensors, the reliability of the sensing means over time due to exposure to weather, and the accommodation of terrain irregularities. A reliable means to sense closure of the towing vehicle and the towed vehicle is subject to the same design considerations. In addition, it is necessary to convey concise guidance information to the operator of the towing vehicle in a way that will allow safe operation thereof.
Several systems, both line guided and otherwise, are known in the prior art for providing guidance information when docking a towing vehicle with a vehicle to be towed. Exemplary of these prior art references are U.S. Pat. Nos. 4,187,494 to Jessee, 3,731,274 to Green, 3,938,122 to Mangus, Re. 28,590 to Salmi, 4,432,563 to Pitcher, 4,186,939 to Woods et al., 4,938,495 to Beasley et al., 4,552,376 to Cofer, and 2,736,885 to Thompson. However, each of these systems is disadvantageous in certain respects.
It is therefore the principal object of the present invention to provide a simple, low cost, yet highly precise guidance system for use in docking a towing vehicle with a stationary target.
This and other objects are accomplished in accordance with the illustrated preferred embodiment of the present invention by providing a sensing unit pivotally mounted about a horizontal axis on a towing vehicle in axial alignment with a hitch member thereof, and a display unit, electrically coupled to the sensing unit, the display unit being mounted on the towing vehicle in view of the driver, either directly or through the use of a rear view mirror. A tensioned line is stored on a spring and reel assembly within the sensing unit and is adapted to be unreeled therefrom and attached to a connection point on the stationary target that is aligned with a hitch member of the stationary target. The tensioned line passes through a movable shutter element of a shutter assembly within the sensing unit. Optical switches within the shutter assembly sense lateral deviations from a position of perfect axial alignment of the tensioned line with the hitch members on both the towing vehicle and the stationary target. Electrical signals from the optical switches are used to appropriately illuminate a plurality of visual turn indicators on the display unit to signal to the driver of the towing vehicle the need for either a left or right turn correction, as required to axially align the hitch members of the towing vehicle and the stationary target. A stop function is provided to visually and audibly signal the driver of the towing vehicle when a predetermined closure distance between the towing vehicle and the stationary target has been reached. A test switch is provided on the display unit to test the operational readiness of the visual and audible indicators thereof. A turn indicator reversing switch is also provided on the display unit to permit the driver of the towing vehicle to view the visual turn indicators either directly or by use of a rear view mirror.